How HR Monitoring Works
The following article is for watches with heart rate monitors, and doesn’t apply to Pebble Classic, Steel, Time, Time Steel or Time Round.
Note: if you haven’t set up Pebble Health yet, you’ll need to. Instructions can be found here.
How It Works
Your heart rate is monitored every 10 minutes, unless you trigger constant monitoring with the Workout App, or by leaving the heart rate card open in the Health App. You may see data from longer than 10 minutes ago if Pebble Health determines a heart rate reading’s quality is poor, as it won’t include that reading.
Pebble HR-enabled devices use optical heart rate monitors, which we’ve tested for accuracy against industry-leading devices (see more on Accuracy below). The monitor works using LED lights, which flash hundreds of times per second.
The amount of light reflected from these flashes tells the monitor how many times your heart is beating per minute. Blood absorbs light from the flashes, so when your heart beats and pumps more blood through your wrist, less light gets reflected; between beats more light is reflected, since less blood is moving past the watch.